Three-dimensional image display apparatus and a screen therefor

ABSTRACT

In the disclosed three-dimensional image display apparatus, a projecting system projects images having parallax information onto a screen. The screen is composed of a plurality of corner reflectors each composed of three intersecting reflecting surfaces, two of which are flat and intersect at right angles to each other in a line perpendicular to a parallax direction of said images and the other one of which is cylindrical with respect to said parallax direction and at right angles to said two surfaces to be placed in optically identical angular relation to said two surfaces. A mask shields the area around the projecting system so that only light reflected transverse to the parallax can be viewed.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application, Ser. No.042,614, filed May 25, 1979, now abandoned which is a continuation ofapplication, Ser. No. 884,845, filed Mar. 9, 1978, now abandoned, whichis a continuation-in-part of application, Ser. No. 372,001, filed June21, 1973, now abandoned, which in turn was a continuation ofapplication, Ser. No. 808,223, filed Mar. 18, 1969 and now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to a three-dimensional image display apparatusand direction-selective reflection screens therefor.

Three-dimensional images can be displayed by projecting a multiplicityof elemental images having parallax information onto adirection-selective reflection screen. One example of a photogramconsisting of a multiplicity of independent and non-overlappingelemental images involves a multiplicity of elemental pictures, recordedin respective film frames of the same scene photographed from differentangles with a stereoscopic camera, or a plurality of standard camerascoupled to create parallax. Each of the elemental pictures correspondsto an image of a large portion of the scene being photographed as viewedby one of a pair of human eyes positioned at a parallactic distance fromthe other. In other words, the multiplicity of elemental pictures hasparallax information. In most cases, the parallax direction ishorizontal. One way of producing a three-dimensional image by projectionof the aforementioned elemental pictures is to set up a number ofprojectors corresponding to the number of the elemental pictures andarranged in the same way as the camera objective lenses were arrangedwhen the pictures were taken, and direct the projector at the samedirection-selective reflection screen so it can be observed at apredetermined position relative to the projectors. Of course, it ispossible to replace the number of projectors with a stereoscopicprojector having a number of projection objectives.

In this specification, the direction between photograhic objectivesduring photography of the elemental pictures or the direction betweenprojecting objectives during projection of the above-mentioned elementalpictures is known as the parallax direction. Specifically, the directionconnecting the eyes of a photographer or the eyes of an observer is theparallax direction. In most cases, when the line connecting thephotographer's eyes or the observer's eyes is horinzontal, the parallaxdirection (or parallactic direction) is usually horizontal.

Various types of direction-selective reflection screens are known. Forexample, that disclosed in U.S. Pat. No. 1,883,291. This screen isconstructed of a network of reflector elements, each of which consistsof two mirrors arranged to intersect at right angles to each other in aline perpendicular to the parallax direction of the image to beprojected thereon. A disadvantage of such a screen in projecting theelemental images is that as the axis of the light beam projected departsfarther and farther away from the axis normal to the planes parallel tothe intersection of the two mirrors, the incident beam is reflectedfurther upward or downward. Hence, a large proportion of the reflectedbeam will not reach the eyes of an observer located at a positioncorresponding to that of the projector. As a result, the brightness ofthe three-dimensional image particularly at the upper and lower portionsthereof is unacceptably reduced. To avoid this phenomenon, it isnecessary that the entire surface of the screen be curved so as to becylindrical with respect to the line parallel to the parallax direction.Such a deformation of the screen, however, will result in an appreciabledistortion of the displayed image.

There is another way to construct the screen having improved reflectionselectivity characteristics without imparting any curvature to theentire surface of the screen. This is accomplished with a network ofso-called cubic corner type reflectors, each of which consists of threeflat reflecting surfaces arranged to intersect at a common point withthe reflecting surfaces at right angles to each other. A light beamincident upon such a screen is reflected back along the incident beamaccurately upon the source of the light beam. Therefore, athree-dimensional image, though displayed on the screen by projectingthe elemental images in the photogram having parallax information,cannot be observed unless the observer is located exactly at theprojector. With a half-mirror positioned in the path of the projectionlight beam between the projector and the screen, the three-dimensionalimage is made observable to the observer only when he is located at theposition symmetrical to the position of the projector with respect tothe half-mirror plane; that is, at the position corresponding opticallyto the position of the projector. It follows that the three-dimensionalimage display system employing the cubic corner type reflector screen ischaracterized by an extremely narrow range of optimum observerpositions. In order for the display system to permit some freedom ofmotion of the head in the vertical direction from the projector inobserving the display, it is necessary to accommodate a number ofadditional projectors superimposed on the existing projector in a planeperpendicular to the parallax direction. This additional projectorarrangement defeats the purpose of minimizing the complexity of thethree-dimensional image display apparatus. Further, the utilization ofthe half-mirror arranged between the projector and the screen causes aconsiderable loss of image-forming light in its reflection therefrom aswell as in its transmission therethrough to the observer.

Cubic corner reflector screens are disclosed in U.S. Pat. Nos. 1,671,086and 1,743,835. These screens are used for purposes of road signs, etc.and have one or more surfaces on each reflector deformed to spread lightin all directions. If such screens were used with adjacent projectorsprojecting complementary parallax images, the light on the screen wouldbe spread in all directions simultaneously. Thus, the light from oneprojector projecting one parallax image becomes confused with the lightfrom another projector projecting another parallax image over the entirescreen. Thus, a three-dimensional image would not be perceived.

SUMMARY OF THE INVENTION

An object of the present invention is to alleviate these deficiencies.

Another object of the present invention is to provide athree-dimensional image display apparatus in which a direction-selectivereflection screen receives a multiplicity of images having parallaxinformation from the projecting means onto the screen which produces athree-dimensional image and permits freedom of motion of the head alonga plane perpendicular to the parallax direction in an upward or downwarddirection from the projecting means in observing the three-dimensionaldisplay.

Another object of the present invention is to provide a noveldirection-selective reflection screen which reflects and diffracts abeam of light rays incident upon the screen from the projecting means inplanes perpendicular to the parallax direction in directions eithercontinuously or discretely deviating from the direction opposite to thatin which said beam is projected, while still permitting the informationrelated to the parallax direction to be retained in the reflected beamof light rays without any disturbance in the horizontal direction.

Another object is to minimize stray or undesirable reflections.

According to a feature of the present invention, a direction-selectivereflection screen comprises a plurality of reflectors, each of whichconsists of three reflecting surfaces arranged to intersect at a commonpoint as in a cubic corner type reflector. A reflector composed of threereflectors at right angles to each other, i.e., a reflectorcorresponding in shape to the interior corner of a cube (a cubic cornertype reflector) may be said to be retroreflective. That is, it reflectslight substantially in the direction from whence it came. A screenuniformly composed of such corner reflectors also may be said to beretroreflective. Light which strikes such a screen is reflected back toits source. In the present feature, two of the reflecting surfaces areflat and intersect at right angles to each other. The third reflectingsurface is cylindrical but is in optically identical angular relation tothe first and second reflecting surfaces. The reflectors of theconstruction described above are arranged in the display surface of thescreen so that the line at which the first and second reflectingsurfaces intersect is perpendicular to the parallax direction of theimage to be displayed thereon. In this arrangement of reflectors,therefore, the third, i.e., cylindrical, reflecting surfaces are curvedaround axes oriented parallel to the parallax direction irrespective ofwhether they are concave or convex. With a screen formed from reflectorsof which the third reflecting surfaces are cylindrical, beams of lightrays carrying images having parallax information incident thereon fromthe projecting means are diffusely relected in planes perpendicular tothe parallax direction in directions continuously deviating from thedirection opposite to that in which the beams are projected.

It is to be understood that each of the above-mentioned screens providereflected beams retaining the parallax information carried on theelemental images without any disturbance in the parallax direction. Uponprojection of a multiplicity of elemental images having parallaxinformation from projecting means onto the screen of the invention, athree-dimensional image can be produced on the screen which isobservable to a pair of human eyes located upwardly or downwardly in arange of distances from the projecting means.

According to another feature of the invention, light shielding meansextend substantially parallel to the recorded images and have alongitudinal dimension parallel to the parallax which embraces theprojecting means and a dimension transverse to the parallax to remove aportion of the light from the screen, and define one or more openingsfor passage of light from the projecting means. The light shieldingmeans remove extraneous light diffused in the parallax direction. Thisfeature is based upon the recognition that some extraneous diffusedlight is concentrated along the parallax direction even with theaforementioned screen and that this diffusion is limited in extent to aband transverse to the parallax direction.

According to another feature of the invention, the projecting meansincludes a plurality of film projectors.

According to still another feature, the projecting means includes aholographic reconstructing system.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become evident fromthe following detailed description when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary sectional view of a direction-selectivereflection screen wherein a fly's eye lenslet network, or lenticularsheet is used.

FIG. 2 is a fragmentary sectional view of a direction-selectivetransmission screen wherein two fly's eye lenslet networks, or twolenticular sheets are used.

FIG. 3 is a perspective view of an arrangement of two curved mirrors atright angles to each other.

FIG. 4 is a schematic side view of a three-dimensional image displayapparatus provided with a screen comprising a plurality of twomirror-type reflectors of FIG. 3.

FIG. 5 is a perspective view of a cubic corner type reflector.

FIGS. 6 and 7 are schematic perspective views illustrating a method ofdisplaying a three-dimensional image on a screen constructed in the formof a network of cubic corner type reflectors of FIG. 5.

FIG. 8 is a perspective view of one example of a reflector forthree-dimensional viewing wherein one of the three reflecting surfacesis tilted from optically true right angle relation.

FIGS. 9 and 9A are perspective views of other examples of a reflectoraccording to the invention wherein one of the three reflecting surfacesis curved from optically true right angle relation.

FIG. 10 is a schematic side view of a three-dimensional image displayapparatus provided with a screen of a network of reflectors of FIGS. 8.

FIG. 11 is a schematic side view of a three-dimensional image displayapparatus embodying features of the invention.

FIG. 12 illustrates the reflection patterns of the screen in FIGS. 9 and9A.

FIGS. 13 and 14 are perspective and elevational views of systemsembodying features of the present invention.

FIG. 15 is a perspective view of a light shield for use with FIGS. 13and 14, and embodying features of the invention.

FIG. 16 is a perspective view of still another embodiment of theinvention.

DESCRIPTION OF PREFERRED EMBODIMENTS

An apparatus for producing three-dimensional images by projecting amultiplicity of images having parallax information requires either areflection type projection screen having the property of directing alight beam incident thereon from projecting means toward an observerlocated on the side on which the projecting means is present in adefinite direction relative to that in which the incident beam isprojected, or a transmission type projection screen having the propertyof directing a light beam incident thereon from projecting means towardan observer located on the side opposite to the projecting means in adefinite direction optically equivalent to that in which the incidentbeam is projected, or a projection screen having at least the propertythat the above-mentioned parallax information carried on the incidentbeam is retained in the exit beams. A screen having such a property isherein referred to as "direction-selective screen".

FIG. 1 shows one type of direction-selective reflection screen whichcomprises a fly's eye lenslet network 19 or a lenticular network sheet19 and a diffusing reflection plate 20. The screen provided with thefly's eye lenslet network has the property of reflecting light beamsincident thereon almost along the incident beam back toward the sourceof light as shown in FIG. 1. By employment of the so-called "anamorphic"lens scheme in the screen, it is made possible to impart into the screena further property of diffusing the reflected beams in planes parallelto a specified direction; for example, in the vertical planes, whilepermitting the incident beam to be reflected without any diffusion inplanes perpendicular thereto, i.e., in the horizontal planes. In thiscase, each of the fly's eye lenslets is curved from the sphericalconfiguration in such a manner that the incident light beam is focusedon the diffusing surface in the horizontal direction, while it issomewhat defocused thereon in the vertical direction. The screenprovided with a lenticular sheet 19 has the further property ofdiffusing the reflected beam in planes parallel to one specifieddirection through an angle which may be varied to a large degree.

As shown in FIG. 2, a direction-selective rear screen is constructedcomprising a pair of fly's eye lenslet networks or lenticular sheets 22and 23, and a transmission-type diffusing plate 21 interveningtherebetween. The optical phenomena of the direction-selective rearscreen are identical to those of the screen of FIG. 1 except that thephenomena are observed on the opposite side to that of FIG. 1.

FIG. 3 shows the structure of a two-mirror reflector improved over thetwo-mirror reflector previously mentioned. The improvement resides inthat the two reflecting surfaces at right angles to each other arecurved so as to be cylindrical with respect to the intersection thereofso as to diffuse the reflected beam of light rays in planesperpendicular to the horizontal direction.

FIG. 4 illustrates a three-dimensional image display apparatus providedwith a screen comprising a plurality of two mirror reflectors 18 of theconstruction shown in FIG. 3. As previously mentioned, the entiresurface of the screen is curved with a predetermined curvature so thatsome distortion of the displayed image inevitably results. Although thisscreen is not free of the conventional drawback, it requires nohalf-mirror in observing the display which would have been required inthe apparatus provided with the otherwise designed two-mirror typereflector screen, because the reflected beams are diffused in planesperpendicular to the parallax direction.

FIG. 5 shows a cubic corner type reflector consisting of threereflecting surfaces 1, 2 and 3 arranged to intersect at a common pointwith reflecting surfaces at right angles to each other. A beam 4incident on such a reflector is reflected three times fromsurface-to-surface and back along the incident beams. In other words,the cubic corner type reflector has the property of reflecting anincident beam of light rays parallel to the path of the incident beamsbut in the direction opposite to that in which the incident beam entersthe reflector. That is, it is retroreflective.

FIG. 6 shows an arrangement of the basic parts of a three-dimensionalimage display apparatus employing a screen 5 comprising a plurality ofcubic corner type reflectors of FIG. 5 arranged in contiguousrelationship. A pair of projectors 6 and 7 which project elementalimages of the same object taken from different positions spaced at aparallactic distance (i.e., a stereoscopic couple) are arranged alongthe parallax direction of the stereoscopic couple and above a beamsplitting mirror, or half-mirror 8 which reflects the elementalimage-bearing beams toward the screen 5. The screen 5 acts as a planereflecting mirror to reflect these two beams back through thehalf-mirror 8 to define two spaced exit pupils where an observer mayplace his eyes 9 and 10 to observe the right and left view images of astereoscopic couple with his right and left eyes 9 and 10 respectively.A three-dimensional sensation is thereby perceived.

The right and left eyes 9 and 10 are in positions symmetrical to thepositions of the exit pupils of the projectors 6 and 7 with respect tothe half-mirror 8. Therefore, without the help of the half-mirror, thetwo elemental image-bearing beams will be projected directly from theprojectors 6 and 7 to the screen and back. Hence, the observer would,without the half-mirror, have to place his eyes at the projectors, orelse, the three-dimensional image displayed on the screen cannot beviewed by him. For the convenience of some motion of his head as hemoves along the projector arrangement line or the parallax direction, itis desirable to employ and arrange many projectors along the parallaxdirection as shown in FIG. 7, because the optimum observation positionsare limited to positions symmetrical to the positions of the projectorswith respect to the plane of the half-mirror.

Aside from its use in projecting a multiplicity of elemental imageshaving only one parallax, the apparatus provided with a large number ofprojectors 11, 12, 13 and 14 may be utilized to project a correspondingmultiplicity of elemental images having complex parallax information ora group of elemental pictures produced so as to have a series ofdifferent parallaxes.

In FIGS. 6 and 7, the apparatus is illustrated using separateprojectors. Of course, these may be replaced by one stereoscopicprojector having a corresponding number of projection apertures arrangedon a common line in predetermined spaced relationship. The photogramconsisting of a multiplicity of elemental images to be projected is notconfined to ones recorded on the photographic film by the use ofstereoscopic cameras, but may be others, such as written patterns andholograms provided that when coupled with each other, they createparallax. The performance of the direction-selective screen in makingthe three-dimensional image observable is to retain the parallaxinformation in the three-dimensional image projected onto the screenfrom the projecting means during the display operation without causingany disturbance thereof. Therefore, whether the three-dimensional imageis to be produced from the elemental images produced by a stereoscopiccamera or from a hologram is not essential for the direction-selectivescreen. For convenience, embodiments of the invention describedhereinbelow are directed to applications wherein a multiplicity ofelemental images produced by a steroscopic camera is projected from acorresponding number of separate projectors.

FIG. 8 illustrates an example of a reflector R1 constituting anelemental part of the screen which is suitable for somethree-dimensional viewing. The reflector R1 consists of three flatreflecting surfaces 2, 3 and 15, two of which, namely, surfaces 2 and 3are arranged to intersect at right angles to each other. The otherreflecting surface 15 is tilted from an optically right angular relationindicated by a non-tilted plane 1, but is placed in optically identicalangular relation to the reflecting surfaces 2 and 3. The reflectingsurfaces 2 and 3 are identical to each other in the geometrical sense.The reflecting surface 15 is illustrated as tilted downwardly from theplane 1 as viewed in FIG. 8, or outwardly of the surfaces 2 and 3. Abeam incident upon the reflector is reflected from surface-to-surface inone of six different orders. Of these, the four orders, namely, 2-3-15;3-2-15; 15-2-3; and 15-3-2 permit the reflected beam to emanate from thereflector only in planes parallel to the direction in which the surface15 is tilted in directions deviating from the direction opposite to thatin which the incident beam enters the reflector. The magnitude ofdeviation depends upon the angle through which the surface 15 is tiltedfrom the plane 1. The other two orders of reflection, namely, 2-15-3 and3-15-2 permit the reflected beam to emanate only in planes perpendicularto the direction in which the surface 15 is titled in directionsdeviating from the direction opposite to that in which the incident beamenters the reflector. If the reflector is oriented in the screen so thatthe direction in which the surface 15 is tilted coincides with thevertical direction and the surface 15 coincides with one generated by astraight line moving in such a way that it is always parallel to thehorizontal direction, the horizontal component of the information of theimage with the incident beam is retained in the reflected beam as far asthe former four orders of reflection are concerned.

FIG. 10 shows an arrangement of the basic parts of a three-dimensionalimage display apparatus employing a screen 16 constructed in the form ofa network of reflectors R1 whose details are shown in FIG. 8. Thereflectors are arranged in the screen in closely fitted relationship asshown in FIGS. 6 and 7. The many reflectors of the network arepreferably of identical dimensions and as small as possible for theimprovement of the resolving power of the three-dimensional images.Preferably, the individual reflectors are of identical angles ofdeviation for the improvement of the image quality. A plurality ofprojectors which project the corresponding plurality of elemental imagesare arranged along the parallax direction which coincides with thehorizontal direction as viewed in FIG. 10. The reflectors are arrangedin the screen 16 with respect to the projector arrangement line so thatthe intersection of the two flat reflecting surfaces 2 and 3 of eachreflector is perpendicular to the parallax direction or the projectorarrangement line, and each of the tilted surfaces 15 coincides with aplane parallel to the parallax direction. In other words, each of thereflecting surfaces 15 are tilted with respect to said parallaxdirection from the plane 1 at right angles to the reflecting surfaces 2and 3. The screen 16 may be composed of reflectors having inwardlytilted surfaces 15 and reflectors having outwardly tilted surfaces 15 inan optional proportion provided that the absolute angles through whichthe surfaces 15 are tilted outwardly or inwardly are preferablyidentical to one another as previously mentioned.

A screen, such as 16, makes it possible for a large proportion of thebeams incident upon the screen from the projectors to be reflected inplanes perpendicular to the parallax direction and in directionsdeviating from the direction opposite to that in which the incidentbeams are projected, and to reach observation fields above and under theprojectors as viewed in FIG. 10. There are sometimes appreciable gapsbetween the successive observation fields in the vertical direction, butthese gaps can be lessened by controlling the sizes of the apertures ofthe projection lens systems of the projectors as the reflected beams aredistributed in a certain range in the vertical direction.

As mentioned, the reflected beams are directed in planes perpendicularto the parallax direction while retaining the parallax information.Therefore, the three-dimensional image is observable to a pair of humaneyes located at distances from the projectors in the directionperpendicular to the parallax direction. Although a small proportion ofthe beams incident upon the screen from the projectors is reflected inplanes parallel to the parallax direction, and make no contribution tothe three-dimensional image display, they have little adverse effect inobserving the display because they are mainly diffused and reflectedback toward the projectors.

In constructing the screen to give it the property of reflecting theincident beams in planes perpendicular to the parallax direction so asto extend the range of observation positions in the vertical directionfrom the projectors while retaining the parallax information in thereflected beams, it is important for each of the reflectors of thescreen that the intersection of the two flat reflecting surfaces 2 and 3at right angles to each other be accurately oriented so as to beperpendicular to the parallax direction of the multiplicity of elementalimages to be projected. It is also important that the reflecting surface15 be accurately oriented so as to be tilted with respect to theparallax direction and so that the tilted surface 15 coincides with onegenerated by a straight line always parallel to the parallax direction.If the surface 15 is tilted regardless of the parallax direction and/orif the intersection of the surfaces 2 and 3 is permitted to assume anoptional attitude regardless of the parallax direction, the reflectedbeams are certainly not concentrated on the projectors only. Rather,they are dispersed in all directions, resulting in disturbance of theparallax information of the multiplicity of elemental images to noteffect three-dimensional image display.

FIGS. 9 and 9A show one example of a reflector 12 constituting anelemental part of a screen 18 in a system embodying features of thepresent invention. The reflector R2 is composed of three reflectingsurfaces 2, 3 and 17, two of which are flat surfaces 2 and 3 and arearranged to intersect at right angles to each other. The otherreflecting surface 17 is curved to progressively deviate from opticallyright angular relation indicated by plane 1, and is placed in opticallyidentical angular relation to the reflecting surfaces 2 and 3. Thereflecting surfaces 2 and 3 are identical to each other in the geometricsense. The reflecting surface 17 is illustrated as convex toward theother two flat reflecting surfaces 2 and 3. But the surface 17 may becurved so as to be concave toward the surfaces 2 and 3. A beam incidentupon the reflector is reflected from surface-to-surface in one of sixdifferent orders. Of these, the four orders, namely, 2-3-17; 3-2-17;17-2-3; and 17-3-2 permit the reflected beam to emanate from thereflector only in planes parallel to the normal of the cylindricalsurface 17 in directions continuously deviating from the directionopposite to that in which the incident beam enters the reflector. If thereflector is oriented in a screen so that the cylindrical surface 17coincides with one generated by a straight line parallel to thehorizontal direction, the reflected beams are diffused only in verticalplanes, and, therefore, the horizontal component of the information ofthe image with the incident beams is retained in the reflected beam asfar as the above-mentioned four orders of reflection are concerned.After an incident beam is reflected in one of the two orders, namely,2-17-3; and 3-17-2, the reflected beam emanates only in planes parallelto the cylindrical surface 17 in directions continuously deviating fromthe direction opposite to that in which the incident beam enters thereflector. This horizontal reflected beam does not retain the horizontalcomponent of the information of the image with the incident beam.Rather, the horizontal component becomes disturbed.

FIG. 9A shows a reflector R2', another form of the reflector R2 in whichthe surface 17' is concave relative to surfaces 2 and 3. This reflectorR2' exhibits the same vertically retroreflective characteristics as thereflector R2.

FIG. 11 shows reflectors R2 or R2' in an arrangement embodying theinvention. Here, a screen 18 is formed from a plurality of thereflectors R2 of FIG. 9. The screen 18 corresponds to the screen 16except for having reflectors R2 instead of R1. The many reflectors R2 ofscreen 18 are preferably of identical dimensions and are as small aspossible for the improvement of the resolving power of thethree-dimensional images. Preferably, the individual cylindricalreflecting surface 17 of all of the reflectors are of identical radii ofcurvature for the purpose of improving the image quality. A plurality ofprojectors P1 to P4 which project the corresponding plurality ofelemental images are arranged along the parallax direction. Thereflectors R2 are arranged in the screen 18 with respect to theprojector arrangement line so that the intersection of the two flatreflecting surfaces 2 and 3 of each reflector is perpendicular to theparallax direction or the projector arrangement line, and each of thecylindrical surfaces has its axis parallel to the parallax direction. Inother words, the surface 17 is curved so as to be cylindrical withrespect to the parallax direction. The screen 18 may be composed ofreflectors R2 having cylindrical reflecting surfaces 17 convex towardthe other two flat reflecting surfaces and reflectors R2' havingcylindrical reflecting surfaces 17' concave toward the other two flatreflecting surfaces in an optional proportion. Preferably the radii ofcurvature of the cylindrical surfaces 17 are identical to one another asmentioned.

With the screen 18 having reflectors R2 and/or R2', a large proportionof the beams incident upon the screen from the projectors is reflectedand diffused in planes perpendicular to the parallax direction indirections continuously deviating from the direction opposite to that inwhich the incident beams are projected. The reflected beams retain theparallax information as mentioned. Therefore, a three-dimensional imageis observable to a pair of human eyes located at distances from theprojectors in the direction perpendicular to the parallax direction.With the screen 18 formed from a plurality of reflectors R2 and/or R2'having cylindrical reflecting surfaces 17 and/or 17', the reflectedbeams are diffused in planes perpendicular to the parallax directionmore widely and uniformly than with the screen 16 formed from aplurality of reflectors having flat tilted reflecting surfaces shown inFIG. 8. Hence, the three-dimensional image display apparatus providedwith the screen 18 constructed in accordance with this embodiment of theinvention permits a certain continuous range of motion of the head inthe direction perpendicular to the parallax direction upwardly ordownwardly from the projectors while observing a good qualitythree-dimensional image. In constructing the screen 18 from theaforementioned reflectors R2 and R2' of FIG. 9, it is important for eachof the reflectors that the intersection of the two flat reflectingsurfaces 2 and 3 at right angles to each other be accurately oriented soas to be perpendicular to the parallax direction of the multiplicity ofelemental images to be projected, and that the axis of the cylindricalsurface 17 or 17' be parallel to the parallax direction. If the surface17 or 17' has its axis parallel in a direction other than the parallaxdirection, and/or if the intersection of the surfaces 2 and 3 ispermitted to assume an optional attitude regardless of the parallaxdirection, the reflected beams are certainly not concentrated only onthe projectors, they are dispersed in all directions, resulting indisturbance of the parallax information of the multiplicity of elementalimages to effect no three-dimensional image display.

In the screen 18 of FIG. 11, which may be called a curved triple mirror(or CTM) screen, the quality of the displayed three-dimensional image issubstantially susceptible to deviations of reflector parameters from thespecific values and errors, or orientation and arrangement of thereflectors in the screen with respect to the parallax direction inassembling a complete screen from the reflector elements. An increase ofdeviations and errors causes deterioration in the direction-selectivityof the screen causing a larger disturbance of the parallax informationof the multiplicity of elemental images in the original photogram.

The screen 18 reflects a portion of the incident beam in planes otherthan those perpendicular to the parallax direction as mentioned. A plateM substantially reduces or virtually eliminates any adverse effect whichthe reflection of an incident beam in planes other than thoseperpendicular to the parallax direction, i.e., the direction about whichthe surfaces 17 or 17' are curved, may produce on the three-dimensionaldisplay. The reflection in directions other than transverse to theparallax direction produces a zone in which three-dimensional imagescannot be observed. This will become evident from an examination ofFIGS. 12 and 13.

FIG. 12 illustrates the reflection patterns formed when a light beam isprojected onto the screen 18 at right angles to the plane of the screen18. In FIG. 12, the corner reflectors are arranged so that the axesabout which the surfaces 17 or 17' curve are parallel to the expectedparallax, i.e., horizontal in this case. The reflection patterns A, B,C, and D are all formed within the plane at right angles to the axis Oof light projected onto the screen 18. The patterns A and B are verticaland transverse to the parallactic axis. With a number ofparallactically-spaced projectors, the patterns A and B are the desiredpatterns for producing the three-dimensional perception by an observer.The patterns C and D are substantially parallel to the parallactic axis,i.e., horizontal, and when formed by a number of projectors oftwo-dimensional parallactic images, do not cause perception ofthree-dimensional images by a viewer. The patterns C and D formspuriously, and hence, undesirable images.

As shown in FIG. 13, when two-dimensional picture images of differentparallaxes for three-dimensional observation are projected on the screen18 by the plurality of projectors P1, P2, P3, and P4, the lightprojected by the projector P1 and reflected by the screen 18 is expandedvertically on the observation plane S, (i.e., the three-dimensionalpicture image position at the projector plane, preferably at theprojector lens) to provide an image observation zone VI. It is alsoexpanded in the lateral direction to provide a horizontal zone H. Theprojectors P2, P3, and P4 form vertical zones V2, V3, and V4, whilesimultaneously forming a horizontal zone H. In this horizontal zone H,where the light is expanded laterally, the images projected by all theprojectors are observed simultaneously. Thus, if the left eye is placedin the zone in which V2 and H overlap and the right eye in the zone inwhich V3 and H overlap, the left eye will observe the images from P2 andP4 in addition to the image from P3. Thus, in the zone H, it is notpossible to observe good three-dimensionality.

The present invention eliminates the light which expands in the lateralor horizontal direction by providing a light shielding plate M in thezone in which the light expands in the lateral or horizontal direction.More specifically, as shown in FIG. 14, the light shielding plate Mhaving openings A1, A2, A3, and A4, through which the projected lightpasses from lenses L1, L2, L3, and L4, is arranged on thethree-dimensional picture image plane so as to eliminate the laterallyexpanding light from the screen 18.

In FIG. 14, the light shielding plate M is in the form of a narrow plateextending in the direction of the arrangement P1 to P4, namely, in thedirection of the parallax. The extent perpendicular to the parallaxdirection, namely, the vertical width of the plate for horizontalparallax is great enough to cover the maximum spurious expansion d inFIG. 12 in the parallactically transverse direction (vertical forhorizontal parallax) of the paralactically expanding (horizontallyexpanding for a horizontal parallax) light. The width in the directiontransverse to the parallax, of the light shielding plate M, must be atleast d/2 above the optical axis of the nearest projector lens, namelyfrom the center of the projected light along the length transverse tothe parallax of the observable zones V1 to V4. If the eyes are alwaysplaced above the projectors, the portion below the projector axis maynot be needed at all. According to another embodiment, the plate M mayextend much further down.

The length of the plate M in the direction along the parallax mustextend at least from the extreme end of the zone V1 and the oppositeextreme end of the zone V4. The plate M effectively removes the lightexpanding in the direction of the parallax and limits the zones V1 to V4to areas in which proper three-dimensional images may be observed.

Preferably, the plate M is made of highly absorbing material, e.g.,coated with light absorbing paint or printed with fibers.

FIG. 15 illustrates another light shielding plate M embodying featuresof the invention. Here, the end portions are turned toward the screen.

The invention is not limited to exhibiting three-dimensional displaysfrom spaced two-dimensional images. Rather, it includesthree-dimensional viewing of a three-dimensional record, such as ahologram by means of the screen 18. This is accomplished by illuminatinga hologram from behind with a reconstructing beam directed toward thescreen 18. The screen 18 then retroreflects the light and expands it.

FIG. 16 illustrates another system embodying features of the inventionand using a light shielding plate. Here, a hologram HO placed in anaperture AP of a horn shaped shield BA is illuminated by areconstructing beam BE from a coherent light source CL. The light fromthe hologram produces a reconstructed image on the screen 18 whichproduces a vertically expanded retroreflective image and a spurioushorizontal pattern near the hologram HO. It is here as well as elsewhereassumed that the parallactic direction is horizontal although this neednot be the case. The light expanded in the parallactic direction fromthe reconstructed image passes through the aperture A1 into the hornbody where it decays.

According to an embodiment, the horn screen of FIG. 16 is used with aplurality of projectors.

While embodiments of the invention have been described in detail, itwill be evident to those skilled in the art that the invention may beembodied otherwise without departing from its spirit and scope.

What is claimed is:
 1. A device for producing a three-dimensionalpicture image, comprising a reflection-type three-dimensional imagedisplay screen having plural reflectors arranged to form an imagedisplay surface, each reflector including three reflecting facesarranged to intersect at a common point, two of said faces being flatand intersecting at right angles in a line perpendicular to the parallaxdirection, the other face of each reflector being parallel to theparallax direction and being cylindrical with respect to an axisparallel to said parallax direction, the curvatures of all thecylindrical reflecting faces being equal in absolute value to oneanother, means for projecting the three-dimensional image recorded on arecording body; a light-shielding arrangement in the plane of therecording body and having an aperture through which light projected fromthe projecting means passes, said arrangement having a size in adirection perpendicular to the parallax direction large enough to removelight expanding from the screen in the parallax direction.
 2. A deviceaccording to claim 1, in which the recording body is composed of aplurality of two-dimensional picture images and the projecting means iscomposed of a plurality of projectors.
 3. A device according to claim 2,wherein the plurality of picture images are projected through theaperture of the light shielding arrangement.
 4. A device according toclaim 1, wherein the recording body is a hologram and the projectingmeans is a hologram reconstructor including a light source.
 5. A deviceaccording to claim 4, wherein the hologram is located in the aperture ofthe light shielding arrangement.
 6. An apparatus for three-dimensionalimage display for an observer's eyes, comprising:projecting means forprojecting a three-dimensional image of an object, a reflecting typescreen having an image display surface, which optically faces saidprojecting means and an observer's eyes located at a substantialdistance from said projecting means in a direction perpendicular to adirection along which the observer's eyes are arranged and defining aparallax direction, and comprising a plurality of reflectors which areformed and arranged in said image display surface so that each reflectorconsists of three reflecting faces arranged to intersect at right anglesto each other in a line perpendicular to said parallax direction, andthe other one of which is parallel to said parallax direction and iscylindrical with respect to an axis parallel to said parallax direction,the curvatures of all the cylindrical reflecting faces being made equalin absolute value to one another, so that light rays incident upon theimage display surface from the projecting means is reflected therefromto the observer's eyes to permit said three-dimensional image to beobservable.